I made a lovely silly mistake yesterday. One of the kind where neither strictures, nor warnings, nor syntax highlighting can help. One of the nasty kind where the code appears to work, and produces a plausible but incorrect result. Something functionally equivalent to:

It must have taken the best part of ten minutes for me to spot the two-character brainfart that was causing that never to process any records...

Seriously, I don't think there's any way to prevent "doh" moments. The best one can hope to do is to prevent those errors that can be prevented, and make sure your tests are comprehensive enough to catch the rest.